1. Field of the Invention
The present invention relates to a ventilation fan and more specifically to a ventilation fan preferably used for cooling electronic equipment, for example, and for other purposes.
2. Description of the Related Art
In recent years, as miniaturization of electronic equipment advances, the density of components in the electronic equipment increases, and thus, the amount of heat generated by the electronic equipment increases. For this reason, a ventilation fan which is mounted on such miniaturized electronic equipment for the purpose of radiating the heat from the electronic equipment is required to be further miniaturized, and to also have a higher cooling ability. In order to satisfy such requirements for the ventilation fan, it is suggested that the rotation speed of the fan may be increased, so as to increase the amount of air flowing through the inside of the electronic equipment.
As a fan motor for driving a conventional ventilation fan, an outer rotor type fan motor in which a rotor magnet is located on the outer side of the stator is often used for the reason of its simple assembling process, among other reasons. However, such an outer rotor type fan may possess a strength problem due to the vibration in high-speed rotation because the moment of inertia in rotation is high.
On the other hand, a fan of inner rotor type in which a rotor magnet is located on the inner side of a stator can perform higher speed rotation because the moment of inertia is lower than that of the outer rotor type.
In a general configuration of a conventional fan of inner rotor type, a shaft (a rotation axis), a bearing arranged to support the shaft, a shaft holding portion arranged to hold the bearing, and a rotor holding portion arranged to hold a rotor magnet are provided in this order from the rotation shaft centre to the outside. However, since it is necessary to provide a certain space between the rotor holding portion as a rotating body and the bearing holding portion as a non-rotating body, there is a limit to miniaturization of such a conventional ventilation fan of inner rotor type with the above-described configuration.